Convective heat transfer within an industrial heat treating furnace

Abstract

An improved heat transfer arrangement for use in a unique multi-function, industrial heat treat furnace which employs a sealed, closed end, heat exchanger shell member containing the work. The heat transfer arrangement includes a totally contained, internal recirculation system which develops an especially configured annular jet stream that produces highly efficient, convective heat transfer with the shell member. After heat transfer between the entrained gases in the jet stream with the shell member has occurred, the jet flow is reversed at one end of the shell and impinged against the workpiece, the spent stream being reformed into the annular jet at the opposite end of the shell member.

Having thus defined my invention, I claim: 
     
       1. A method for effecting heat transfer within an industrial heat treat furnace having a sealable, cylindrical, imperforate shell member disposed within a furnace casing for receiving workpieces placed therein for heat treating therein, said method comprising the steps of: (a) changing the temperature of the wall of the shell member so that it is at a temperature different than the temperature of the work within said shell member;   (b) providing a plenum chamber within and at one end of said shell member;   (c) generating an annular jet stream of entrained furnace atmosphere from said plenum chamber through an annular orifice in said plenum chamber having an outside diametrical dimension smaller than the inside diameter of said shell member;   (d) providing an under pressure zone between said annular orifice and said cylindrical shell member;   (e) expanding said jet stream radially outwardly into contact with the interior surface of said shell member as said jet stream travels the length of said shell member from said plenum chamber to the opposite shell end for effecting heat transfer between said shell member and said jet stream, said jet stream when expanded into contact with said shell member forming a laminar flow stream adjacent said cylindrical shell member and a turbulent flow stream radially inwardly of said laminar flow to promote heat transfer of said entrained atmosphere with said shell member.   
     
     
       2. The method of claim 1 further including the steps of diverting the jet stream at said opposite end into a smaller annular jet stream, and impinging said smaller jet stream against said work to effect heat transfer therewith, said smaller stream becoming spend after impact therewith. 
     
     
       3. The method of claim 2 further including the step of collecting a substantial portion of said spend stream within said plenum chamber and pressurizing said spent stream as said annular jet stream. 
     
     
       4. The method of claim 3 further including the steps of admitting a heat transfer gas within said plenum chamber, said spent stream representing the composition of said atmosphere gas within said shell member, and mixing said heat transfer gas with said atmosphere gas as said annular jet travels along the inside cylindrical surface of said shell member. 
     
     
       5. The method of claim 1 wherein said annular jet stream flows generally in a laminar pattern adjacent the inside surface of said shell member as it travels the length thereof and said jet stream flows generally in a turbulent manner radially inwardly of said laminar pattern.